Wireless communication systems have been widely deployed to provide various types of communication services such as voice or data. In general, a wireless communication system is a multiple access system that supports communication of multiple users by sharing available system resources (a bandwidth, transmission power, etc.) among them. For example, multiple access systems include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, and a multi-carrier frequency division multiple access (MC-FDMA) system.
Device-to-device (D2D) communication refers to a communication scheme in which a direct link is established between user equipments (UEs), and voice and data are directly transmitted and received between the UEs without intervention of an evolved Node B (eNB). D2D communication may include UE-to-UE communication and peer-to-peer communication. Further, D2D communication may be applied to machine-to-machine (M2M) communication, and machine type communication (MTC).
D2D communication is considered as a solution to reduce the burden of an eNB, caused by rapidly increasing data traffic. For example, since data is transmitted and received between devices without intervention of an eNB in D2D communication, unlike a legacy wireless communication system, the overhead of the network can be reduced. In addition, it may be expected that the introduction of D2D communication will bring about the effects of simplified procedures in an eNB, reduction of the power consumption of devices participating in D2D communication, increased data rates, increased accommodation capability of a network, load distribution, and extension of cell coverage.
At present, vehicle to everything (V2X) communication is under discussion in conjunction with D2D communication. V2X communication conceptually covers vehicle-to-vehicle (V2V) communication between vehicle terminals, vehicle-to-pedestrian (V2P) communication between a vehicle and another type of terminal, and vehicle to infrastructure (V2I) communication between a vehicle and a roadside unit (RSU).